This invention relates to a control system for synchronizing a combination press line which is comprised of a transfer press and a double-action press.
In a combination press line comprised of a transfer press and a double-action press, in order to achieve an automatic operation of the press line it is necessary to synchronize press cycles of both presses because there exists a mutual interference range between an unloader of the double-action press and transfer feed bars of the transfer press. Since the combination press line of the type described above is new in the field, there has been no system for synchronizing the particular combination press line. There have been disclosed, however, many ways for synchronizing the operation of a series of presses which usually include several presses but not a transfer press.
One of such systems is disclosed in U.S. Pat. No. 3,199,439 to J. C. Danly. The system disclosed in this patent employs a master control means having a variable speed motor independent of presses in the press line and all the presses are to be synchronized with the movement of the variable speed motor. Therefore there is no master-slave arrangement among the presses in this patent, rather all the presses are considered to be slaves to the master control means provided outside of and independent of the presses. The master-slave arrangement referred to in the specification means that one of the presses in the press line is selected as the master and all of the other presses follow it as slaves.
In this control system, however, because the master control means provided independent of any presses in the press line controls synchronization of the press line, even if synchronization allowance between two presses is plus or minus 20.degree. of cycle, each press must be operated with synchronization allowance being plus or minus 10.degree. of cycle with respect to the master control means in order to avoid interference between the two presses. That is, synchronization allowance is slashed to half in this kind of control system wherein no master-slave arrangement is employed.
Therefore the system must employ more complicated and sophisticated arrangements leading to an expensive overall control system.
Moreover, since the variable speed motor of the master control means rotates at a constant speed, it is necessary for main motors of the presses in the press line to have powers 1.5 to 1.8 times bigger than those required to drive presses in order to follow the master control means.
There have also been known control systems for synchronizing the operation of a series of presses taking master-slave arrangements.
It should be recognized, however, that those control systems are specifically adapted for controlling a series of presses in a press line and not adapted for controlling a combination press line having a transfer press and a double-action press.